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Role of Protein Oxidation in Water-binding and Hydration of Meat
Department of Animal and Food Sciences
The ability of meat to retain natural and added moisture during storage and cooking critically affects meat juciness, tenderness, and mouthfeel. The purpose of the study is to learn how oxidation affects water-binding in meat through analyzing morphological and biophysical properties of muscle and muscle proteins.
2009 Project Description
The overall objective of the proposed study is to elucidate the morphological/structural changes in oxidatively stressed myofibrils and in their main constituting proteins, and to understand how such modifications contribute to water-binding and hydration of meat. In 2009, three graduate students and one research associate participated in this project.
Progressive results summarized in two abstracts were presented at the 2009 Institute of Food Technologists (IFT) annual meeting in Anaheim, California. In addition, an update of the research progress was presented at the 2009 NRI Project Director (PD) meeting in conjunction with the annual IFT conference. A significant output is the publication of one journal article resulting from the study. The PDs meeting provided a unique forum for the interaction and idea exchange among delegates and audiences representing food companies, government agencies, consumer groups, and other universities to share major discoveries from this research project. In 2009, the PD visited a research lab at a university in China that was also studying protein oxidation. A mutual agreement for collaboration was reached.
Two experiments were conducted. In experiment 1 (completed), myofibrils isolated from fresh pork longissimus muscle were exposed to a hydroxyl radical-generating system (0.01 mM iron chloride, 0.1 mM asorbate, 1 mM hydrogen peroxide) for up to 12 h at 2° C. In experiment 2 (in progress), myofibrils were extracted from commercial fresh ground pork stored at 2°C in an oxygen enriched packaging system (MAP, with 80% oxygen and 20% carbon dioxide). Packaging with polyvinylchloride (PVC) wrap was used as control for comparison. Oxidation-induced changes in the hydration properties of myofibrils was investigated by irrigation of myofibrils with brines (0.1-0.8 M NaCl, 10 mM pyrophosphate, 2 mM MgCl2, pH 6.0).
Morphological changes and structural alterations, including the dissolution of myofibrils and the removal of myosin, in oxidation-stressed and control (nonoxidized) myofibril samples during hydration were examined by phase contrast microscopy. Results from Experiment 1 showed that irrigation with >0.4 M NaCl produced marked swelling of nonoxidized myofibrils and concomitant dissolution of the myosin filaments from both sides of the A-band. However, such structural changes were somewhat suppressed in oxidized myofibrils. Oxidized myofibrils had a reduced myosin and actin extractability and lost some contractability due to disulfide bond formation between myofilaments. Results from Experiment 2 demonstrated that drip loss increased during storage of all meat samples and there was no difference due to packaging conditions. The A-bands in myofibrils disintegrated more extensively upon brine irrigation at >0.4 M NaCl for fresh meat samples than for stored samples (7 days for PVC; 14 days for MAP) at 2° C, due to oxidation of both proteins (carbonyls) and lipids (TBARS).
These findings indicated that reduced water-holding capacity of fresh pork stored in MAP or exposed to an oxidizing environment was due to reduced structural expandability and protein extractability of myofibrils. Oxidative modification of proteins was implicated. Although the impact of the research results is not immediately known, it is expected that meat processors can use the research findings as guide for their product formulation and processing condition design so that an optimal product quality and yield can be achieved.
Xiong, Y.L., Park, D., and Ooizumi, T. 2009. Variation in the cross-linking pattern of porcine myofibrillar protein exposed to three oxidative environments. Journal of Agricultural and Food Chemistry 57:153-159.
Ma, Y.Y., Xiong, Y.L., J. Zhai, H. Zhu, and Dziubla, T. 2010. Fractionation and evaluation of radical-scavenging peptides from in vitro digests of buckwheat protein. Food Chemistry 118:582-588.
Liu, Z., Xiong, Y.L., and Chen, J. 2010. Identification of restricting factors that inhibit swelling of oxidized myofibrils during brine irrigation. Journal of Agricultural and Food Chemistry 57:10999-11007.